Fin-stabilized mortar shells are generally fired by inserting them from above into the barrel of the weapon. The fin-stabilized mortar shell or grenade has an ogival body and slips through the barrel as far as the lower end thereof. After ignition of the propellant charge, the shell is propelled out of the barrel. A certain amount of play with comparatively large tolerance is necessary between the zone of greatest diameter of the ogival body and the inside of the diameter of the barrel so that the shell can slide in the barrel with the known type of propelling charge. However, because of the annular clearance around the outside of the caliber diameter zone of the body, the propellant gases in the known devices are capable of passing through forwardly into the free space formed in that annular clearance. Consequently, the propellant gases after passage of the shell through the body cannot contribute to the firing of the shell.
Known fin-stablized shells include annular grooves which have been arranged in the greatest diameter zone or caliber diameter zone to form an eddy zone and thus a baffle effect for the propellent gases arriving from the explosion of the charge. The eddy zone and baffle effect hinders the flow of the propellant gases and thereby prevent the gases from penetrating forwardly of the caliber diameter zone. The baffle effect of the gases also sets up a zone of pressure which slows down the oscillating movement of the shell during its passage through the barrel. The propellant gases may be held back with greater or lesser efficiency through the particular formation of the cross section of the annular grooves.
It is further known to place a sealing ring in the annular groove which is located within the limits of the caliber diameter zone of the shell body. The sealing ring is effective to seal the shell body with respect to the inner wall of the barrel against the propellant gases flowing from behind. Such a known ring is split and therefore is spreadable outwardly against the inner wall of the firearm barrel. Such a prior art sealing ring, however, may not project beyond the greatest diameter of the ogival shell body. Otherwise, difficulties arise with respect to the loading of the shell when attempting to insert it from above into the firearm barrel. Obviously, the loading operation of the mortar barrel must proceed completely in an uninterrupted manner. When the sealing ring is in the relaxed condition, it must not project beyond the outer diameter with the annular groove. This, however, leads to the difficulty of reliability with respect to the spreading of the sealing ring so that the propellant gases acting from behind the ring are effectively held back against their penetration forwardly of the ring.